Neutron beam characterization at the Intense Pulsed Neutron Source

The Intense Pulsed Neutron Source (IPNS) at Argonne National Laboratory is a spallation neutron source dedicated to materials research. Its three cryogenic methane moderators provide 12 neutron beams to 14 neutron scattering instruments and test facilities. The moderators at IPNS are of cryogenic methane (CH4): one of liquid methane at 100 K and two of solid methane at 30 K. These moderators produce intense beams of both cold and thermal neutrons. The moderators are each of a different physical configuration in order to tailor their performance for the instruments and facilities that operate on the neutron beams. As part of the ongoing operation of IPNS, as well as new enhancements to the target, moderator, and reflector systems, the authors have performed experiments characterizing the energy and time distribution of neutrons in the various beams. These measurements provide absolutely normalized energy spectra using foil activation techniques joined with time-of-flight (TOF) measurements and energy-dependent time distributions using a time-focused crystal analyzer